There are some types of image forming apparatuses for continuously printing both sides of a recording medium, including opposing printing heads with a recording medium conveyance path interposed therebetween.
Such types of image forming apparatuses generally include thermal heads disposed in the vicinity of upstream and downstream in a recording medium conveyance direction. The thermal heads are disposed opposite to a platen with the recording medium conveyance path interposed therebetween. The recording medium is conveyed by rotation of the platen. The conveyance of the recording medium requires rotating the platen with the thermal heads pressurized to the platen.
However, when the recording medium is discharged, if the thermal head in the upstream in the recording medium conveyance direction continues to be pressurized to the platen even when a tailing end of the recording medium escapes from the thermal head, then the thermal head may be worn out by contact with the platen.
Further, to print a leading end of the recording medium, there is a need to move the recording medium forward or backward to adjust a printing position. In such a case, if the thermal head in the downstream in the recording medium conveyance direction continues to be pressurized to the platen until the recording medium arrives at the thermal head, then the thermal head may be worn out by contact with the platen.
Moreover, when the recording medium is removed from the image forming apparatus, it becomes difficult to draw the recording medium out if the thermal heads continue to be pressurized to the platen.
In this regard, there has been proposed a technique that can adjust a pressurizing force of a head using a cam.
However, two sets of thermal heads and platens require a more complicated control.
Accordingly, there is a need of head pressurizing force adjusting device, an image forming apparatus and a head pressurizing force adjusting method, which can change a pressurizing force of thermal heads depending on conditions of the image forming apparatus.